It is narrated from Sayyiduna Abu Uthman (may Allah be pleased with him) that Sayyiduna Anas bin Malik (may Allah be pleased with him) came to us when we had already prayed Fajr; he gave the adhan and the iqamah, then led his companions in the Fajr prayer.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 1918